Hardfacing has been used for many years on earth-boring bits to reduce the abrasive and/or erosive wear. The hardfacing typically comprises hard metal particles dispersed within a metal matrix. The hard metal particles are often formed of tungsten carbide. Sintered tungsten carbide, also called cemented carbide, comprises tungsten carbide grains within a binder powder, such as cobalt. The tungsten carbide grains utilized in sintered tungsten carbide pellets are generally less than ten microns in diameter. During this sintering process, which employs heat and pressure, the cobalt will enter a liquid stage while the tungsten carbide grains remain in the solid stage. As a result of this process, the cobalt cements the tungsten carbide grains to create sintered tungsten carbide. The ductile cobalt metal offsets the characteristic brittleness of the tungsten carbide particles, resulting in a pellet that has enhanced toughness and durability. Sintered tungsten carbide pellets can be formed into generally spherical shapes or irregular shapes. Also, sintered tungsten carbide in a crushed form is available.
Cast tungsten carbide particles are formed in a casting process, and, thus, are harder than sintered tungsten carbide and do not have a binder of a soft metal such as cobalt. Cast tungsten carbide particles may be spherical, irregular or crushed. Spherical cast carbide pellets are typically smaller in diameter than standard spherical sintered tungsten carbide pellets. Cast tungsten carbide particles are thus harder than sintered tungsten carbide particles but more brittle.
Prior art hardfacing for earth-boring bits contains a variety of sizes and volume fractions of standard spherical sintered tungsten carbide pellets, crushed sintered tungsten carbide particles, spherical cast tungsten carbide pellets, crushed cast tungsten carbide particles, as well as other types of cast tungsten carbide, such as monocrystalline or macrocrystalline particles. The matrix that contains and binds the hardfacing pellets and particles is often iron, but it also may contain nickel and/or other alloys.